A steering assist apparatus applied to a vehicle and performing a control to assist a driver with a steering operation has been conventionally known (refer to Japanese Patent Application Laid-Open (kokai) No. 2009-274594). This control to assist the driver with the steering operation (hereinafter, this control is also referred to as a “steering assist control”) includes, for example, a lane tracing assist control (hereinafter, also referred to as “LTA”), a lane changing assist control (hereinafter, also referred to as “LCA”), and the like.
The LTA is a control to assist (support) the driver with the steering operation such that a traveling position of the vehicle is kept at a predetermined position in a lane in a lane width direction based on lane information including a relative positional relationship of the vehicle with respect to the lane. The LCA is a control to assist the driver with the steering operation such that the vehicle changes a lane from an original lane on which the vehicle is currently traveling to a target lane adjacent to the original lane based on the above lane information. Hereinafter, a vehicle in which the steering assist apparatus is mounted is also referred to as an “own vehicle”.
More specifically, in the steering assist control such as the LTA and the LCA, a steered angle of each of steered wheels is controlled in such a manner that a yaw angle (an angle formed by a direction along which a lane is formed and a direction toward which the own vehicle is oriented) coincides with a target yaw angle. It should be noted that the target yaw angle for the LTA is zero degree.